One of the .NET Framework 3.0 or 3.5 prerequisite packages requires that the Print Spooler service is running in the "Started" State. If the Print Spooler Service is not running, the .NET Framework 3.0 or 3.5 installation will fail.
To resolve this issue
Start the Print Spooler service before...

Commonly this is caused by the installation program you've downloaded to become corrupted in the download. By redownloading to either a different location you should be able to fix this issue.
Another common remedy for this issue is to download the redistributable package corresponding to your architecture...

This is a common question on the .NET Framework Setup Forum.
Let me first answer this by YES!!! ABSOLUTELY!!! WE DESIGNED IT THAT WAY!!!!
Ok now that is out of the way, I would like to explain why. .NET Framework 3.0 is built on the .NET Framework 2.0 Libraries.
The following link is from MSDN...

A. Visual Studio 2005 will target your managed appliations as 2.0 by default. 3.0 adds to the 2.0 layer and is fully backwards compatible. For more information check out the following link:
http://msdn2.microsoft.com/en-us/netframework/aa663309.aspx
If you want to compile 3.0 projects then you...